Method of quantifying the quality of service in a CDMA cellular telephone system

ABSTRACT

A process which determines all locations in a service area which are subject to interference-causing limitations, assigns an average service level to each such location, sums the service levels at all such locations, and divides the sum of the service levels at all such locations by the total service level for the service area to produce an interference value.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to cellular telephone systems and, moreparticularly, to processes for quantifying the performance of CDMAcellular telephone systems.

2. History of the Prior Art

Presently available commercial mobile communication systems typicallyinclude a plurality of fixed base stations (cells) each of whichtransmits signals to and receives signals from mobile units within itscommunication area. Each base station is assigned a plurality ofchannels over which it can communicate with mobile units. A mobile unitwithin range of the base station communicates with the external worldthrough the base station using these channels. Typically, the channelsused by a base station are selected so that signals on any channel donot interfere with signals on another channel used by that base station.

In order to allow mobile units to transmit and receive telephonecommunications as the units travel over a wide geographic area, eachcell is normally physically positioned so that its area of coverage isadjacent to and overlaps the areas of coverage of a number of othercells. When a mobile unit moves from an area covered by one base stationto an area covered by another base station, communication with themobile unit is transferred (handed off from one base station to anotherbase station in an area where the coverage from different cellsoverlaps.

It is axiomatic that cellular telephone transmissions between the mobileunits and the cells should be as free from interference as possible. Themanner in which this is accomplished differs depending on thecharacteristics of the particular cellular system.

In the most prevalent American Mobile Phone System (AMPS) system,channels are defined by frequency. A frequency band providingapproximately four hundred different adjoining FM frequency channels isallotted to each cellular system operator. In a typical AMPS system,each channel uses a fixed FM frequency band for downlink transmissionfrom a base station to a mobile unit and another fixed FM frequency bandfor uplink transmission from a mobile unit to a cell. Typically, thefrequencies assigned to the downlink transmissions for an entire AMPScellular system immediately adjoin one another and are widely separatedfrom the frequencies assigned to the uplink transmissions which alsoimmediately adjoin one another.

Since channels are defined by frequency in an AMPS system, interferencewith any particular transmission is essentially due to transmissions onthe same or immediately adjacent channels. To reduce this interference,an operator assigns channels to any single base station which areseparated from one another in frequency sufficiently to eliminateinterference between those channels. For example, an operator may allotto a base station a set of channels with frequencies which are eachseparated from the next by some large number (e.g., twenty-one) channelscarrying intermediate frequencies.

Moreover, since a mobile unit in an AMPS system moving from an areacovered by one base station to that covered by another base station mustbe transferred from one base station to the other in an area in whichcell coverage overlaps, interference with base stations havingoverlapping cell coverage must also be eliminated. To do this, thechannels allotted to the adjoining cells are carefully selected toeliminate the same frequencies. This is sometimes accomplished byassigning channels to a central cell which are widely separated infrequency in the manner described above, and then assigning channels tothe cells surrounding that central cell using a pattern which increaseseach channel assignment by some number for each sequential cellsurrounding the central cell. This produces what may be visualized as ahoneycomb pattern of cells having a central cell surrounded by a numberof overlapping cells transmitting on different frequencies. The samehoneycomb pattern extends outward throughout the system with each cellsurrounding the central cell functioning as a central cell surrounded byits own overlapping cells producing what is referred to as a reusepattern. In such a pattern, interference on the same channel usuallycomes from cells at some distance from the cell carrying the usefulinformation.

In most cellular systems, especially those with cells in urban areascarrying heavy traffic, a position at which a cell is situated includestwo or three individual transceiving stations (referred to as “sectors”)each of which may include channels having the above-described frequencyallotment of channels. The antennas of each sector are typicallyarranged to provide 180 or 120 degree coverage. The terms cells,sectors, and base stations are normally used interchangeably in thisspecification unless the context indicates otherwise. If an AMPS systemincludes significant numbers of sectored cells, six cells arranged in ahoneycomb pattern surrounding a central cell may all be assigneddifferent and theoretically non-interfering channels. However, outsidethe initial central cell and its immediately surrounding cells, thefrequency reuse pattern requires that channels be replicated at muchcloser ranges than in a non-sectored system.

In another common type of mobile system called Time Division MultipleAccess (TDMA), frequencies are assigned to the entire system in groupsmuch like they are assigned in an AMPS system. However, within anyfrequency, each base station sends and receives in bursts during somenumber of different intervals or time slots. These time intervals withinfrequency bands then effectively constitute the individual channels. Byusing these intervals and assuring that the group of frequenciesassigned to any individual base station differ from one another and fromthe frequencies assigned to base stations surrounding each individualbase station, a channel reuse pattern is established which allowssubstantially greater use of the frequency spectrum because of the timedivision process.

A newer type of mobile system called Code Division Multiple Access(CDMA) uses encoded digital signals to transmit data. All of the basestations and mobile units of a CDMA system presently use the same“spread spectrum” frequency band of 1.25 megacycles to transmit theencoded digital signals although other band widths are presentlyproposed. The information bits of each transmission are expanded usingcoding information called a pseudo noise (PN) code. Each sectorthroughout a system uses the same PN code to encode the informationtransferred. Then each sector identifies itself by using a time offset(generally referred to as a pseudo noise (PN) offset) from somerepeating initial time in the expanded transmission. Thus, one sectormay begin an encoded transmission at the initial time, a second sectorat an offset of one unit from the initial time, a third at an offset oftwo units, and so on up to a total of 512 offset units. Eachtransmission with a sector is placed on what is effectively a separatechannel by further encoding the expanded transmission with one of aplurality of Walsh codes. A Walsh code is a mask used to encode anddecode transmissions which eliminates transmissions sent using otherWalsh codes. A transmission on a particular channel is decoded byapplying a mask including the Walsh and PN codes to the received patternof information bits commencing at the PN offset designated for theparticular channel.

The CDMA system of transmission offers a number of advantages. One ofthese advantages is that a mobile unit may be receiving the sameinformation from a number of different cells or sectors at the sameinstant. Since all transmissions take place on the same frequency band,a mobile unit actually receives all of the information which isavailable within its range. However, it only decodes information onchannels which are directed to it. A CDMA mobile unit uses a receiverwhich is able to apply a number of decoding masks at the same instant tothe entire spectrum of information which it receives. By knowing theWalsh codes and PN offsets defining channels which it desires toreceive, a mobile unit may decode information from a single message sentto it by a number of different base stations simultaneously and combinethat information to produce a single output message. Thus, while asignal from one sector may be fading, the same message may be receivedwith adequate strength from another sector. This allows CDMA to offerthe possibility of significantly better transmission.

In both AMPS and TDMA system, it is possible to reduce interferencebetween channels by effecting frequency reuse plans in the mannerdescribed above. In theory, these forms of cell arrangement and channelassignments allows channel reuse patterns to be repeated at distancesseparated sufficiently to negate interference between mobile units onthe same and adjacent channels.

Unfortunately, for a number reasons interference does occur in AMPS andTDMA systems even with well chosen frequency reuse plans. Antennapatterns, power levels, scattering, and wave diffraction differ fromcell to cell. Buildings, various other structures, hills, mountains,foliage, and other physical objects cause signal strength to vary overthe region covered by a cell. Consequently, the boundaries at which thesignal strength of a channel falls below a level sufficient to supportcommunications with a mobile unit vary widely within a cell and fromcell to cell. For this reason, cells adjacent one another do not, infact, typically form the precise geometric boundaries suggested above.Since cell boundaries must overlap to provide complete coverage of anarea and allow handoff and because the boundaries of cells areimprecisely defined, signals will often interfere with one another eventhough they are generated by cells which are at distances theoreticallysufficient to eliminate interference. This is especially true when asectored cell pattern is used because the cells are much closer to oneanother than in a simple cell pattern.

In an AMPS system, a first signal on a channel from a remote cellinterferes with a second (usually) stronger signal carrying a mobiletransmission on the same channel within the coverage area of a cell whenthe drop in strength of the first signal from the second signal is lessthan some threshold level (typically 18 decibels). A signal from anothercell on a channel at a frequency adjacent the frequency of a channelcarrying a mobile transmission interferes when the drop in strength ofthe interfering signal from the serving signal is less than some secondthreshold level (typically 6 decibels).

Historically, in order to determine whether interference exists in anAMPS system, a mobile system operator relied on customer complaints.When customers register a sufficient number of complaints regardingcommunication at particular points in a system, an operator usuallyconducts a relatively expensive field test of the suspected portion ofthe system to measure signal strengths received from different cells.During the test, the portion of the system in which the tests areconducted is essentially disabled. Because of the expense andinconvenience, the tests are typically limited only to the suspectedarea. Because such tests are limited to determining the interference atthose points at which a system operator expects to find interference,the efficacy of these tests is very suspect. A major problem with theprocess is that it does not provide a complete understanding ofinterference which actually exists in a system since typically onlythose positions at which extensive interference has been reported aretested. The process does not take into consideration all of the possiblesignals which might be propagating into the affected area to interferewith the carrier nor does it take into consideration the effects which achange in channel assignments may have in other areas of the system.Often (and possibly usually) this method of curing interference merelyexports the interference to another portion of the system where it isonly discovered when a sufficient number of complaints arise to warranta field test of the newly isolated area of interference. Moreover, thismethod of eliminating interference is quite slow and labor intensive.Testing a medium sized system to eliminate interference may require aslong as 400 man hours. The process greatly increases the costs withoutguaranteeing that interference will be eliminated. Because of theemerging nature of the market for cellular telephones, system changeswhich cause interference such as traffic growth are taking placeconstantly and at an accelerating rate.

Recently, a process has been devised by which the quality of serviceprovided by an AMPS or TDMA system (and portions thereof) may bedetermined in terms of fixed verifiable quantities so that changes maybe made to enhance the quality of service with an expectation that thechanges will have the desired result in actually improving the qualityof service provided by the system. The process utilizes data gatheredduring a drive of a service area during which transmitted signalstrength and received signal strength at each location throughout theservice area are obtained. These values provide actual data from whichall locations at which interference may occur may be determined. Knowingthe locations at which interference may occur allows values to beassigned to a particular service area by which an operator may quantifythe quality of service and decide whether changes in the system arenecessary. This process is described in U.S. patent application Ser. No.08/887,101, entitled “Method of Improving the Operation of a CellularTelephone System”, E. Jensen et al, filed Jul. 2, 1997, and assigned tothe assignee of the present invention.

Theoretically, in contrast to other types of systems, a CDMAtransmission should be interference free throughout the system sincedata is decoded from digital information using masks which are supposedto eliminate interfering signals. However, in a CDMA system alltransmissions are carried by bits transmitted on the same frequencyspectrum. Because of this, information received by a mobile unit or acell is effectively interference if the information is not directed tothat particular receiver. That is, since a receiver receives all of thetransmissions generated by any transmitter within range, theuntranslated transmissions constitute interference in a CDMA system.Typically, before decoding, the desired transmission should have astrength not less than minus 14 dB when compared to the total strengthof all transmissions being received. When the strength of the desiredtransmission falls below this point, the digital details of the messagecannot be retrieved from the spectrum.

Encoding the signals provides a significant encoding gain because eachbit of information is expanded by the pluralities of bits in each of thelevels of coding. A decoded transmission of approximately 7 dB greaterthan interference present after decoding is just sufficient to providesignals of sufficient quality.

Because of the difference of the meaning of interference in thedifferent types of cellular systems, the method of the above-mentionedpatent application for quantifying the quality of service in AMPS orTDMA systems is not as useful when applied to CDMA systems.Consequently, interference in CDMA systems is typically eliminated atpresent by increasing the number of sectors when the transmissions witha sector increase beyond to a particular maximum number. However, it hasbeen determined that such a criteria has very little to do with whetherany particular sector is capable of handling additional transmissions ornot. Adding sectors to a system is an expensive way of handlinginterference.

Consequently, it is desirable to provide a new process by which thequality of a CDMA cellular system may be quantified so that steps may betaken to improve the system.

SUMMARY OF THE INVENTION

The present invention is realized by a computer implemented processwhich determines all locations in a service area which are subject tointerference-causing limitations, assigns an average service level toeach such location, sums the service levels at all such locations, anddivides the sum of the service levels at all such locations by the totalservice level for the service area to produce an interference value.

These and other features of the invention will be better understood byreference to the detailed description which follows taken together withthe drawings in which like elements are referred to by like designationsthroughout the several views.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a CDMA cellular telephone system which may utilize the methodof the invention.

FIG. 2 is a flow chart illustrating a process in accordance with thepresent invention.

FIG. 3 is a flow chart illustrating a particular embodiment of a processin accordance with the present invention.

FIG. 4 is a diagram illustrating a process by which data is accumulatedto be utilized in practicing the invention.

DETAILED DESCRIPTION

Referring now to FIG. 1, there is illustrated a CDMA cellular telephonesystem 10 which includes a number of individual base stations 12arranged to provide coverage of a service area. Each base station 12 inFIG. 1 is illustrated having an outer boundary 13 which indicates theeffective limit of its communication range. The boundaries 13 ofdifferent adjacent base stations typically overlap.

Each of the base stations 12 includes at least one cell which transmitsand receives communications with mobile units 15 operating within itsservice area. In many cases, a base station includes two or threesectors each of which includes communication equipment for communicatingwith a number of mobile units in an area defined partially by an antennapattern angle of 180° or 120°, respectively, from the base station. Alltransmissions between a base station and mobile units in a CDMA systemare digitally encoded and are carried on the same “spread spectrum”frequency band of 1.25 MHz. The digital information bits of eachtransmission are expanded using various levels of coding information.One such level is called a PN code. Each sector throughout a system usesthe same PN code to encode the information transferred. Then each sectoridentifies itself by using an offset (generally referred to as a pseudonoise (PN) offset) in the expanded transmission from some repeatinginitial point typically established through communication with a globalpositioning system. Thus, one sector may begin an encoded transmissionat the initial time, a second sector at an offset of one unit from theinitial time, a third at an offset of two units, and so on up to a totalof 512 offset units. Each transmission with a sector is placed on whatis effectively a separate channel by further encoding the expandedtransmission with one of a plurality of Walsh codes. A transmission on aparticular channel is decoded by applying a mask including the Walsh andPN codes to the received pattern of information bits commencing at thePN offset designated for the particular channel.

The CDMA system of transmission offers a number of advantages. One ofthese advantages is that a mobile unit may be receiving the same messagefrom a number of different cells or sectors at the same instant. Sinceall transmissions take place on the same frequency band, a mobile unitactually receives all of the information which is available within itsrange. However, it only decodes information on channels which aredirected to it. A CDMA mobile unit uses a receiver which is able toapply a number of decoding masks at the same instant to the entirespectrum of information which it receives. By knowing the channels whichit desires to receive, a mobile unit may decode information from asingle message sent to it by a number of different sectorssimultaneously and combine that information to produce a single outputmessage. Thus, while a message from one sector may be fading, the samemessage may be received with adequate strength from another sector. Thisallows CDMA systems to offer the possibility of significantly bettertransmission.

Even with its advantages, CDMA systems do have problems. One of these iscaused by the fact that all transmissions occur on the same frequencyspectrum. Since all transmissions take place on the same frequency band,a mobile unit actually receives all of the transmissions which areavailable within its range. Those transmissions which are not directedto the particular receiver tend to conceal the desired transmissions.When the level of transmissions which are not directed to the particularreceiver reaches a level greater than 14 dB more than the level ofdesired signals before decoding, it becomes difficult to decode thedesired transmissions.

Moreover, although the information directed to the mobile is decodedusing both a PN code mask at a particular PN offset and a Walsh codemask, these masks cannot completely reject all of the unwantedcommunications received. Transmissions paths vary in length, andsufficient leeway must be provided to detect signals directed to themobile unit. This leeway allows interference through the decoding masks.The important element in providing good quality transmissions in a CDMAsystem is to maintain the strength of the desired transmission at alevel greater than 7 dB above the level of all interference receivedafter decoding.

In fact, CDMA systems include features for automatically increasing anddecreasing power levels at the sectors and mobile units in order toassure clear transmissions. A mobile unit measures the strength ofsignals by measuring the rate at which errors occur in signals received(the frame rate error). When errors rise above a prescribed limit, amobile unit signals the sector to increase the strength of itstransmission. The sector does this, but then incrementally decreases thesignal strength from the higher level until the sector is again alertedto raise the strength of the transmission. Thus, when the signal fallsto a level where the frame error rate becomes too high indicating astrength below 7 dB above the interference level, the sectorautomatically increases the power of the signal being transmittedthereby raising the received signal level with respect to interferenceand increasing the signal quality.

In a similar manner, a sector measures the strength of signals receivedfrom a mobile unit by monitoring frame error rate and indicates to themobile whether to raise or lower the strength of its transmission. Whena mobile unit is in contact with a number of sectors, the mobile unitreceives signals from all of the sectors indicating whether to raise orlower its transmission strength. The mobile unit responds to any signalto lower the strength of its signal since a single strong signal issufficient to provide interference free service for the mobile. In doingso, the mobile unit attempts to keep its transmissions at a minimumsignal strength sufficient to provide high voice quality.

Because of this power control, the signal strength from desiredtransmissions with respect to the total received signal shouldtheoretically be equal throughout a service area. In fact, as long asthe ability to utilize power control exists, the ability to add channelsand users without decreasing the quality of service exists.Consequently, many sectors already serving a large number of users arevery capable of adding channels and users without increasinginterference in their transmissions with mobile units. However, theability to adjust power levels cannot function if either the mobile orthe sector has reached any of various maximum power levels so that it isnot able to respond to the power control signals. In such a case,transmissions in the system may be subject to interference so that thequality of service suffers.

More particularly, each sector is assigned a maximum signal strengthlevel for all transmissions and cannot raise its signal strength if itis transmitting at the maximum level. Each sector is also limited to amaximum signal strength for any individual signal transmitted to amobile unit. In a like manner, each mobile unit is limited in the amountof power it can transmit. Consequently, whenever any of these powermaximums is reached, the system is unable to adjust power in order toeliminate interference.

It would be very useful to be able to provide a quantitative evaluationof the quality of service likely to be experienced in a CDMA servicearea. For example, in an AMPS system, it is possible to measure theactual strengths of all signals to be transmitted between a plurality ofcells and a mobile unit at a plurality of locations over an entiremobile communications system, relate data indicating the actualstrengths of all signals to the physical locations from which thesignals are to be transmitted, identify cells transmitting signals ableto serve each location, compare frequencies used at any cell serving alocation with frequencies used at other cells to identify cellstransmitting signals which might interfere with signals transmitted bycells serving a location, determine whether frequencies used at any cellserving a position interfere with frequencies used at other positionsover the entire mobile communications system, and quantify thatinterference over the system.

Unlike AMPS and TDMA systems, however, it is not a simple matter ofmeasuring the strengths of all signals received at a particular locationon the same frequency, comparing those strengths to determine whetherinterference may occur at a location, and summing locations exhibitinginterference to determine the quality of the service.

All transmissions which are received at any location in a CDMA systemare on the same frequency. There may be a very large plurality oftransmissions received at the same time at any location. Most desiredtransmissions are self-adjusting with respect to undesired transmissionsso that useful messages may be received. There is no simple manner ofdetermining where problems with interference may exist.

The present invention provides a process for evaluating the quality ofservice provided by a CDMA system so that an operator may take steps toimprove the quality of service.

The process is described in the flow chart of FIG. 2. The process firstidentifies all locations (measurement locations 17 are illustrated inFIG. 1) at which degraded service can be expected throughout the system.This is accomplished by determining whether one of the three problemswhich cause degradation in a CDMA system exists. If the maximum powerfor the sector transmitter amplifier has been reached, the maximumsector power allotted by a sector to an individual transmission has beenreached, or the maximum mobile power has been reached, then thatlocation is one which may exhibit degraded service.

In order to accomplish this determination, data relating to signalstrength at locations throughout the service area are utilized. This maybe the same data gathered for use in an AMPS or TDMA system utilized inthe same area. Or it may be data accumulated specifically forquantifying the quality of CDMA service in the service area. In anycase, the specific data utilized is data indicating transmitted signalstrength of a transmission at a sector, received signal strength of thetransmission at a location, and the location of receipt. In general,each of these values is accompanied by timing data which helps to relatesignals to sectors and locations.

This data may be collected as is illustrated in FIG. 4 by a mobile unitdriving an area with a scanning receiver and having means (typically acomputer) for logging received signals against time and position. In anAMPS system, such data should be collected while a large portion of theservice area is closed down so that each sector may transmit on a singlefrequency different from frequencies used by other sectors. This allowstransmitting sectors to be identified and the strength of thetransmission to be determined.

In a CDMA system, such data may be collected using a spread spectrumreceiver (called a PN scanning receiver) capable of decoding the PNoffset transmitted by a sector. The spread spectrum receiver measuresthe strength of pilot signals continuously transmitted by base stationson a control channel (the pilot channel) defined by a specific Walshcode. These pilot signals allow mobile units to determine sectors withwhich they should be in contact. When a pilot signal is detected on thepilot channel, the arrival time of the transmission is compared to thesystem initial time provided on another “synchronization” controlchannel to determine the PN offset of the transmission. Using the PNoffset, the transmitting sectors can be identified; and the strength ofthe transmission received at the location from any sector may bedetermined. All of this data is accumulated and stored by a computerassociated with the spread spectrum receiver gathering the data.

Once the data has been accumulated, it may be manipulated by computersoftware designed in accordance with the present invention in the mannerdescribed below. FIGS. 2 and 3 which describe the flow of the operationshould be consulted to better understand this description.

With the strength of both the signal transmitted and the signal receivedavailable, path loss for each transmission from any sector to anylocation is determinable.

In computing the quality of service in a CDMA system, the measuredstrength of all transmissions arriving at each location (made up of thepilot signals, other control signals, and signals directed for users)may be summed to provide the total received strength at the location.The sum of the received strength of all signals at a locationconstitutes the interference level at the location (referred to asN_(o)). The strength of a pilot signal Eb which must be received at thelocation to provide a quality signal can then be determined as a decodedsignal above a level just greater than 7 dB above the total interferencelevel N_(o) (after decoding). Of course, the specific level may vary inaccordance with the equipment actually utilized in the operation.

The minimum signal strength necessary at a location may then be added topath loss between the location and a sector to determine a transmittedsignal strength which is necessary for the channel at the sectortransmitter. If this power is not available, then the sector has reacheda maximum for a channel, and the location is an interference problem forthe sector.

During the operation of computing the strength of transmissions fromeach sector, a running total of the strengths of transmissions from eachsector for all locations may be accumulated and summed to determine foreach sector whether total sector power is at a maximum. If so, a sectorcannot provide adequate signal strength for the plurality of mobileunits it must service resulting in it being an interference problem forthe system.

Finally, to determine whether the mobile transmitter must provide morethan its maximum power in order to furnish a quality signal from alocation to a sector, the sum of all received (interfering)transmissions at a sector is determined. From this sum, a value which is7 dB above this sum is computed to determine the minimum received signalstrength necessary at the sector for a quality signal. This minimumreceived signal strength plus the path loss to the location provide avalue indicating the signal strength which must be available at themobile unit. If this value is greater than the maximum power availableat the mobile unit, then the location is an interference problem forthat sector. By computing such a necessary transmission value for eachsector with which the location is expected to communicate, it may bedetermined whether the location poses an interference problem for eachof the sectors in the system with which it could be expected tocommunicate.

Once all locations which may exhibit degraded service have beenidentified, the number of such locations is summed for the service area.This sum is multiplied by an average traffic level determined fromexpected traffic for the service area. If a service area is to provideservice for ten mobile customers, for example, and there are a total ofone hundred locations in the service area, then each location may beexpected to have an average traffic level of {fraction (1/10)}th of acustomer. This average traffic level multiplied by the number of problemlocations provides a value for problem locations in the service area.

In an alternative embodiment, the various locations throughout a systemare assigned traffic levels depending on historical and perspectiveevaluations of the amount of traffic that particular location has or islikely to experience. Then the traffic level for all of the problemareas in the service area is summed to reach a total value.

The total value for problem locations in the service area is thendivided by the total number of expected users for the service area todetermine a score for the service area which represents a percentage ofproblems for the area given the number of expected users. This score maythen be compared to scores for other service areas to determine whetherthe particular service area is one which should be modified to improvethe system. It should be noted that the particular service area may bethe entire system, a portion of the system, or a service area for asingle sector.

It should be noted that the use of data actually acquired by driving thesystem eliminates the need to make estimations based on environmentalmodels not necessarily representative of any particular system. Themethod of the invention also allows the system to utilize data which isuseful for many different levels of usage and to vary the levels ofusage while determining the quality of service for the particularservice area. This allows planning for service areas without the need toregather data.

Although the present invention has been described in terms of apreferred embodiment, it will be appreciated that various modificationsand alterations might be made by those skilled in the art withoutdeparting from the spirit and scope of the invention. The inventionshould therefore be measured in terms of the claims which follow.

What is claimed is:
 1. A method of quantifying the quality of service ina CDMA cellular telephone system comprising: dividing a service areainto a total number of locations served by a service area; identifyingsubstantially all locations in a service area having degradedoperations, wherein said identifying comprises: determining a level oftransmitted signal required from each base station to each location atwhich signals are expected based upon said received signal levelnecessary for providing a quality transmission at the location and pathloss between the location and each base station; summing the levels ofall transmitted signals from each base station; and comparing the sum ofthe levels of all transmitted signals from each base station to themaximum transmission power of the base station; assigning an averageservice level value to each location having degraded service torepresent a level of service at the location; summing the averageservice level values of each location in the service area havingdegraded operations; determining the level of service throughout theservice area; determining the ratio of said locations receiving degradedservice to said total number of locations served by said service area toobtain a value representing the quality of service for the service area;dividing the sum of the average service level values by the level ofservice throughout the service area to obtain a value representing thequality of service for the service area.
 2. A method as claimed in claim1, further comprising: assigning a value representative of the expectedlevel of service to each location comprising degraded service; andcombining said assigned values of levels of service at each location inthe service area at which degraded operations may be expected to obtainan overall value representative of service degradation.
 3. A method asclaimed in claim 2, further comprising: determining a probability ofservice value for each of said total number of locations served by aservice area; combining the probability of service values for each ofsaid total number of locations to obtain an overall probability ofservice value; and dividing said overall value representative of servicedegradation by said overall probability of service value to obtain saidvalue representing the quality of service for the service area.
 4. Amethod of quantifying the quality of service in a CDMA cellulartelephone system, comprising: dividing a service area into a totalnumber of locations served by a service area; identifying substantiallyall locations in a service area having degraded operations, wherein saididentifying comprises: determining total interference for each locationin the service area from data defining signals received at the location;determining a received signal level necessary for providing a qualitytransmission at each location; determining path loss between eachlocation and each base station; determining a level of transmittedsignal required from each base station to each location at which signalsare expected based upon said received signal level necessary forproviding a quality transmission at the location and path loss betweenthe location and each base station; and comparing maximum channeltransmission power to the level of transmitted signal required;assigning an average service level value to each location havingdegraded service to represent a level of service at the location;summing the average service level values of each location in the servicearea having degraded operations; determining the level of servicethroughout the service area; determining the ratio of said locationsreceiving degraded service to said total number of locations served bysaid service area to obtain a value representing the quality of servicefor the service area; and dividing the sum of the average service levelvalues by the level of service throughout the service area to obtain avalue representing the quality of service for the service area.
 5. Themethod as claimed in claim 4 in which said identifying substantially alllocations in a service area having degraded operations furthercomprises: summing the levels of all transmitted signals from each basestation; and comparing the sum of the levels of all transmitted signalsfrom each base station to the maximum transmission power of the basestation.
 6. A method of quantifying the quality of service in a CDMAcellular telephone system, comprising: dividing a service area into atotal number of locations served by a service area; identifyingsubstantially all locations in a service area having degradedoperations, wherein said identifying comprises: determining totalinterference for each base station in the service area from datadefining signals received at the base station; determining a receivedsignal level necessary for providing a quality transmission at each basestation; determining path loss between each location and each basestation; determining a level of transmitted signal required from eachlocation to each base station at which signals are expected based uponsaid received signal level necessary for providing a qualitytransmission at the base station and path loss between the location andeach such base station; and comparing channel transmission power to thelevel of transmitted signal required; assigning an average service levelvalue to each location having degraded service to represent a level ofservice at the location; summing the average service level values ofeach location in the service area having degraded operations;determining the level of service throughout the service area;determining the ratio of said locations receiving degraded service tosaid total number of locations served by said service area to obtain avalue representing the quality of service for the service area; anddividing the sum of the average service level values by the level ofservice throughout the service area to obtain a value representing thequality of service for the service area.
 7. A method as claimed in claim6, further comprising: assigning a value representative of the expectedlevel of service to each location comprising degraded service; andcombining said assigned values of levels of service at each location inthe service area at which degraded operations may be expected to obtainan overall value representative of service degradation.
 8. A method asclaimed in claim 6, further comprising: determining a probability ofservice value for each of said total number of locations served by aservice area; combining the probability of service values for each ofsaid total number of locations to obtain an overall probability ofservice value; and dividing said overall value representative of servicedegradation by said overall probability of service value to obtain saidvalue representing the quality of service for the service area.